1. Field of the Invention
The present invention generally relates to analysis and display of data acquired using computed tomography representing various organs of the human body. More specifically, the present invention relates to a computerized system for analyzing data acquired from tubular structures of the body, for example, the colon or gastro-intestinal tract, and displaying that data in a manner providing for rapid evaluation of the tissue structures of tubular structure and the accurate determination of any abnormalities present.
2. Description of Related Art
In industrialized nations, colorectal cancer is the second leading cause of deaths from malignancy. In the United States, almost 150,000 people are determined to have colon cancer annually. Unfortunately, colon cancer also causes approximately 60,000 deaths annually, with only lung cancer causing more deaths among the population of America. What makes these statistics truly unfortunate is that colon cancers are perhaps one of the most preventable of cancers because they usually begin as benign polyps which grow slowly for five to ten years before becoming cancerous. If these polyps are detected and removed, the risk of developing colon cancer is greatly reduced.
Regrettably, widespread colorectal screening and preventive efforts are hampered by several practical impediments, including limited resources, methodologic inadequacies, and poor patient acceptance leading to poor compliance. In addition, a fecal occult blood test (FOBT) fails to detect the majority of cancers and pre-cancerous polyps. Since sigmoidoscopy only examines a portion of the colon, it also misses many polyps. The accuracy of barium enema varies among centers and is therefore not always reliable.
Therefore, there is a need for a new test which can be used to screen for pre-cancerous colon polyps, as well as other abnormalities, such as the thickening of the colorectal wall caused by tumors that might otherwise not be found. Like all screening tests, this new test must be relatively inexpensive, minimally invasive, and highly specific.
A technique using helical (also known as spiral) computed tomography (CT) to create computer simulated intraluminal flights through the colon was proposed as a novel approach for detecting colorectal neoplasms by Vining D J, Shifrin R Y, Grishaw E K, Liu K, Gelfand D W, Virtual colonoscopy (Abst), Radiology Scientific Prgm 1994; 193(P):446. This technique was first described by Vining et al. in an earlier abstract by Vining D J, Gelfand D W, Noninvasive colonoscopy using helical CT scanning, 3D reconstruction, and virtual reality (Abst), SGR Scientific Program, 1994. This technique, referred to as “virtual colonoscopy”, requires a cleansed colon insufflated with air, a helical CT scan of approximately 30-60 seconds, and specialized three-dimensional (3D) imaging software to extract and display the mucosal surface. The resulting endoluminal images generated from the CT scan data are displayed to a medical practitioner for diagnostic purposes.
The technique of reformatting 2D cross sections perpendicular to the colon midline is also described in U.S. Pat. No. 5,458,111, issued Oct. 17, 1995 to Coin. However, direct interpretation of the cross-sectional images is difficult because a scan of the colon consists of several hundred axial tomograms. Without advanced image manipulation tools, interpretation of the colon's complex three-dimensional shape from these cross sections alone is very difficult for a medical practitioner.
One approach to improve accuracy involves production of reformatted 2D images at cross sections and orthogonal angles to the colon midline. These reformatted 2D images can provide complimentary diagnostic information when viewed with corresponding intraluminal 3D images. Exam efficiency can be improved with innovative 3D rendering techniques that allow fast, interactive evaluation on low priced computer hardware.
While these techniques have advanced the art of using CT scanning in assisting the diagnosis of colorectal cancers, among other diseases, the prior techniques typically required massive computing capacity and specialized work stations. Moreover, the prior techniques have also been limited to providing views of the colorectal pathway that may occlude the presence of polyps, and which do not provide any information regarding the subsurface morphology of the colorectal pathway, or other tubular structure being analyzed. Typically, the only views provided to the physician or technician viewing the data display are two and three-dimensional endoluminal, coronal, sagittal and axial views of the tubular structure being evaluated.
Generally, a CT scanner and computer workstation are used to image tubular structures of the human body, such as the digestive tract of a living person. The CT scanner is used to generate cross-sectional axial images of a human colon which are then transferred to the computer workstation. A colon midline is defined which follows the colon lumen. The computer workstation supports colon midline definition by generating and displaying reformatted cross-sectional images, volume rendered scouts, and interluminal views. Semi-automatic midline defining tools may also be included. After the midline is defined, a montage of images is displayed for diagnostic purposes. The images include axial sections, transluminal cross section, and intraluminal volume rendered images.
Semiautomatic methods are used to delineate the three-dimensional shape of the colon by identifying its approximate midline. This is supported by the display of coronal, sagittal, and axial views as well as an off-axis plane orthogonal to the midline. Straightened curved sections along the midline and a rendered view from the end of the midline may also be displayed. Editing the midline in any of these views will typically cause the other views to update accordingly. After the midline of the colon is traced, data are extracted so the colon can be examined efficiently.
In general practice using the equipment described above, a medical practitioner, such as a radiologist, examines a tubular structure of a patient, such as the patient's colon, by moving a virtual view point along the delineated midline. Three-dimensional orthogonal off-axis cross sections, volume rendered extra-luminal scouts or the original axial 2D images, and a high resolution perspective rendering of the colon's inner surface may be displayed so that the practitioner can observe the structures of the tissues of tubular structure being analyzed. The perspective views can typically be re-oriented in any direction. A rotatable longitudinal sectioning along the colon's midline may also displayed. This view, which may be advanced along the entire length of the colon, enhances both navigation of the path forward or backward along the 3D images and interpretation of the 3D images.
Experience has shown that the simultaneous display of cross-sectional and rendered views enhances diagnostic interpretation of the CT data more than either cross-sectional or intra-luminal views alone. Volume rendering of the CT data is performed by custom algorithms that use pre-computation of texture and other techniques to achieve interactive performance on moderately priced workstations.
Commonly, at least two views of the three-dimensional images generated as described above are displayed to the practitioner. The first view is typically a forward intra-luminal view which encompasses a view of the colon from the view point looking away from a terminating location of the colon, such as the anal verge. The second view may be a backward intra-luminal view which encompasses a view of the colon from the view point looking toward a terminating location of the colon, such as the anal verge. Displaying both views makes it less likely that a feature of interest will be obscured due to the topology of the colon.
By pointing the cursor on the image and simultaneously pressing a key or otherwise issuing an appropriate instruction to the computer work station, a practitioner can move the view point off the previously defined midline, and all images, including 2D reformatted images, 3D intra-luminal images, and the 2D axial image may be updated to views corresponding to the designated position. The practitioner can randomly move the view point by using the pointing device, or return to the nearest point on the predetermined midline.
To assist in diagnosis, an unfolded or opened view of the colon may also be displayed to the observer. The opened view of the colon corresponds to a view of the entire colon as if it had been physically divided and opened for inspection, just like cutting a garden hose in half along its longitudinal axis, maintaining the curvature of the colon. However, this “unfolding” technique only allows a view of the internal structure of the tubular structure or colon, and does not provide a truly “flattened” view of the internal wall of the colon, wherein the inherent curvature of the colon is “flattened”, thus allowing structures that protrude from the inner wall of the colon, such as Haustral ridges, to hide structures such as small polyps or other anomalies from the practitioners view.
Moreover, none of the systems, methods or techniques currently available are believed to be able to provide an assessment of the wall of the tubular structure. For example, some colorectal cancers do not grow out of polyps, but instead manifest themselves within the walls of the colon. Such cancers cannot be observed using the means described above, since none of those methods allow for an analysis of the wall thickness or density of the tubular structure.
What has been needed, and heretofore unavailable, are techniques which provide efficient and accurate presentation of CT data that provided a flattened view of a tubular structure that prevents structures within the tubular structure from obscuring the view of anomalies such as polyps in a colon. Moreover, such techniques should be able to run efficiently and quickly on commonly available computer platforms, such as on computers manufactured by Apple or on IBM clones. Additionally, such a system should be able to also analyze anomalies present in the wall of the tubular structure, such as variations in wall thickness or density that may indicate the presence of tumorous growths or other disease. The present invention satisfies these and other needs.